Hubble and Nearby Stars

[ZenGalacticore]

M.Wayne- Have they ever used the Hubble to do long exposure surveys of the nearby stars? It seems like since they can image galaxies hundreds of millions of light years away with such clarity and resolution, that they could get some pretty cool images at least of the Alpha Centauri system, being only a little over 4 lys away.

I of course realize that a galaxy is hundreds of billions of times more massive than a single star and therefore much brighter, but I would think they could still get some good images of stars in our immediate neighborhood.

 

[MeteorWayne]

The problem is that that except for the very closest and largest stars, they are still just a point of light. A single pixel. So while you might get an image of the 3 stars, they would still be unresolvable points of light. Remember, Alpha Centauri (the largest) is just a borderline dwarf star like our own sun. The other two in the system are smaller, and much smaller. The next 3 closest stars are dim red dwarves, and again would be pixel sized. After that comes the Sirius pair, which are very bright and about twice as far away.

Something like the Andromeda Galaxy is scores of times larger than the full moon, so the light gathering ability, exposure time, and resolution of the Hubble can gain a lot. I'm not sure that is true about tiny stars like the Centauri triplet. Remember, the Hubble is not a really big mirror, in fact by earth standards it's rather puny. So especially with nearby stars, earth based telescopes with much larger apertures will get you more resolution (in other words, being able to resolve a disk, at least a little bit). What hubble has going for it is the clearest and most undisturbed imaginable "sky", and the ability to take long exposures with no need for adaptive optics.

I am not sure if Hubble has ever imaged either system (a Cen or Sirius), I'll have to search a bit.

But it's not really what it's best at.

BTW, there was a fascinating article in Nature or Science in the last month about a wide scale survey of the Andromeda galaxy (M31) and it's satellite M33 showing dozens of dwarf galaxies and their remains that it has eaten. I meant to start a thread on it. I'll have to dig it out and do that.

MW

 

[ramparts]

Let's run some numbers to see this (after all, it's a science forum!). The angular diameter of a star is roughly given by its radius divided by its distance, in radians. If we use WolframAlpha, we see:

http://www.wolframalpha.com/input/?i=%2 ... rc+seconds

that for a Sun-sized star at 1 light year (so closer than Alpha Centauri), the size is about 0.02 arcseconds, or .000004 degrees on the sky. Tiny. Hubble's angular resolution is, best as I can tell, about 0.05 arcseconds, so even at its best Hubble still wouldn't be able to make it out - it would be smaller than one of Hubble's pixels, as MW said.

 

[MeteorWayne]

Thanx ramparts...I don't have to formula at hand, but had good reaon to believe I was right.

Still, an image of the Alpha Centauri system from Hubble would be cool. I'm not sure it would be a good use of the telescope's time (since it is parceled out so judiciously), so I'm still searching.

 

[kg]

M.Wayne- Have they ever used the Hubble to do long exposure surveys of the nearby stars?....

For high resolution in the visible spectrum the Keck Interferometer is I think the best instrument ( I might be wrong). It can't resolve features on the surface nearby stars but it can remove much of the light from the star to reveal dust or possibly even exoplanets close to the star that would be otherwise lost in the stars glare.
Here are a couple of links you might find interesting.
http://planetquest.jpl.nasa.gov/Keck/keck_project.cfm
http://en.wikipedia.org/wiki/Keck_Interferometer

I seem to remember reading about someone gleening some sort of data about the surface of stars by examining the stars light curve during the transits of exoplanets. Maybe someone else has more information on that?
http://en.wikipedia.org/wiki/Transiting ... sit_method

 

[ramparts]

kg, the transiting thing is a different ballgame. Even if you can't angularly resolve a star's surface, by observing its brightening and dimming it is (in theory) possible to figure out some stuff about starspot cycles and the like.

 

[MeteorWayne]

M.Wayne- Have they ever used the Hubble to do long exposure surveys of the nearby stars?....

I seem to remember reading about someone gleening some sort of data about the surface of stars by examining the stars light curve during the transits of exoplanets. Maybe someone else has more information on that?
http://en.wikipedia.org/wiki/Transiting ... sit_method

Concindentally there's an article about that very subject (work done by amateurs) in the October Sky and Telescope.

 

[ZenGalacticore]

Thanks for the info Wayne and everybody.

Well I think it's high time we deploy some multi-mirrored 'bug-eyed' optical telescope complexes on the Moon. That would give us more reason for going back.

I've heard that these multi-mirrored instruments(say 10 or 20 mirrors acting in tandem) would be capable of some seriously clear, visual spectrum images.

 

[MeteorWayne]

From what I understand there's one big problem on the moon; lunar dust. From what I've read it is levitated by the charge differential between sunlight and darkness which moves with the terminator. Eventually, it would cover the mirrors with a thick enough layer to require cleaning, and as anyone with a telesope knows, cleaning a mirror is no trivial matter.

That's just my recollection though.

 

[ZenGalacticore]

That sounds logical to me, kind of like static attracting dust, I guess. But hey, again that would give justification for maintaining a permanent presence on the Moon!!

At any rate, some multiple mirrored bug-eyed scopes in orbit would be nice!

Btw, some time ago-a couple of years at least- I read about a binocular telescope being developed, IIRC, by a Japanese/American partnership that supposedly would have been able to see better than Hubble. Anything to that?

 

[kg]

....Well I think it's high time we deploy some multi-mirrored 'bug-eyed' optical telescope complexes on the Moon.... [/m quote]

The point multi-mirrored design as well as many other features of the Keck tellescope is to deal with the distorting effects of the atmosphear and provide a "cheap" alternative to a telescope deployed in space.

 

[MeteorWayne]

It's more than just the adaptive optics, kg. It's also far easier and less expensive to cast a number of smaller mirrors rather than one large one. There are only a few facilities than can make really big single mirrors, and they are very expensive.

 

[ZenGalacticore]

....Well I think it's high time we deploy some multi-mirrored 'bug-eyed' optical telescope complexes on the Moon.... [/m quote]

kg wrote- The point multi-mirrored design as well as many other features of the Keck tellescope is to deal with the distorting effects of the atmosphear and provide a "cheap" alternative to a telescope deployed in space.

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That should make multi-mirrored scopes all the more acute in space beyond atmosphere. Yes?

 

[kg]

That should make multi-mirrored scopes all the more acute in space beyond atmosphere. Yes?

I'm glad your a fan of space telescopes! Have you read anything about the James Webb Space Telescope? Keep an eye on this, it will be AMAZING if they get it off the ground!!

http://en.wikipedia.org/wiki/James_Webb ... ope#Optics
"....The observatory is due to be launched no earlier than June 2014...."
"Although JWST has a planned mass half that of the Hubble, its primary mirror (a 6.5 meter diameter gold-coated beryllium reflector) has a collecting area which is almost six times larger. As this diameter is much larger than any current launch vehicle, the mirror is composed of 18 hexagonal segments, which will unfold after the telescope is launched."

There are many advantages and disadvantages to putting a telescope in space. You generally need a compelling reason to go through all the expense and risk, such as observing in wavelenghts that are blocked by the atmoshere. There have been many excellent telescopes put in space (besides the Hubble) to observe gamma rays, x-rays, ultra violet, infrared, etc... Its very difficult and expensive to work the bugs out of a telescope or fix it or upgrad it once it's in orbit! But yes the seeing is unbelievably clear once you get up there. We are very fourtunate that NASA has paid so much attention to the Hubble these last couple decades.

 

[ZenGalacticore]

Yes. I've read of the Webb Space Telescope. It promises to easily equal Hubble and surpass it in many ways, IIRC. And over the years I've read about the myriad of other scopes up there that observe in the different wavelengths, but it's hard to keep track of them all.

Off the top of my head I can remember COBE, the background rad scope, and... what is it, INRA the infra-red radio interferometer, I think?

I love astronomy but I also have many other interests: natural history, history, anthropology, art, archeology, political sci, etc.. You know what I mean? So it's hard these days to remember everything I read, which kind of sux!

But yes I am all for more and better space telescopes. The Kepler promises to do some great observational science too, and I hope I live to see the next generations of scopes coming after it and Webb. It seems to me, that if we put our minds and wallets to it, within a generation or so we could be not only imaging earth-sized planets, but detecting tell-tale signs of life on distant worlds as well. 'Earth-shine' and other signatures of sustained O2 atmospheres and indications of plant life. Very exciting to be in these times!!